Effects of P and B adsorbates on the Fe(111) surface

To gain insights into the segregation energy differences between grain boundaries and free surfaces which drive impurity embrittlement of boundaries, the effects of P and B adsorbates on the Fe(111) surface have been determined using the all-electron full-potential linearized augmented-plane-wave total-energy method. The calculated nearest P(B)-Fe distance in P(B)/Fe(111) is 2.14(1.82) {}. Both P and B affect the surface relaxation of the Fe(111) substrate strongly. In contrast to the P-Fe bonding, there is no evident charge transfer from B to Fe. The dangling B pz bonding toward the vacuum side suggests that B is more stable in the grain boundary environment. Although the adsorption energy for B is slightly smaller compared to that for P (7.1 versus 7.6 eV), B enhances while P weakens the cohesion of Fe grain boundaries since B has a much larger binding energy (1.4 eV) in the grain boundary than does P.